An amine compound, 4,4′-diamino-3,3′-dichlorodiphenylmethane as a raw material for urethane resins, is generally referred to as MOCA or MBOCA and is used in the production of urethane foam for abrasive and polishing pads (for example, Japanese Patent Application, First Publication No. H2-232173 (Example 1) and Japanese Patent Application, First Publication No. 2002-194104 (claim 1, and Example 1 in paragraph [0034])).
The polishing pad disclosed in Japanese Patent Application, First Publication No. H2-232173, for example, is prepared in the following manner. Water (foaming agent) and an epoxy resin powder are added to a toluene diisocyanate (TDI)-based urethane prepolymer, followed by addition of a catalyst, a silicone oil and 4,4′-diamino-3,3′-dichlorodiphenylmethane (hereinafter also referred to as MBOCA). The mixture is cast in a mold using a casting machine, is foamed and thereby yields a block molded article. The block molded article is sliced to yield the polishing pad.
In this procedure, a two-component mixing casting machine is generally used. This is because MBOCA used herein has a melting point of about 110° C., water has a boiling point of 100° C., and the reaction between the urethane prepolymer and MBOCA (crosslinking reaction) and the reaction with water (foaming reaction) must occur simultaneously. In this molding process, MBOCA must be heated to 110° C. or higher so as to liquefy MBOCA to be suitable for mixing. In contrast, water serving as the foaming agent must not be incorporated into the isocyanate urethane prepolymer in advance, since water reacts with the isocyanate. Thus, water is added to MBOCA in advance. However, water evaporates upon heating of MBOCA at 110° C., i.e., the melting point of MBOCA, or higher so as to liquefy MBOCA. Thus, a desirable foam is not prepared. More specifically, the resulting foamed molded article exhibits increased density variation and lacks uniformity in density distribution which is essential to an abrasive.
Japanese Patent Application, First Publication No. 2002-194104 discloses a molded article prepared by, instead of foaming with water, mixing a prepolymer having a terminal isocyanate group with fine particles treated with a silicone surfactant, adding MBOCA to the mixture and casting the resulting mixture into a mold. Even treated with a surfactant, however, such fine particles are difficult to be uniformly mixed with the prepolymer having a terminal isocyanate group, failing to yield a molded article having a uniform density distribution.